Radius end mill

ABSTRACT

In the radius end mill, main gash faces has an angle of inclination with respect to an axis that is smaller than a twist angle of chip discharge flutes. The main gash faces are formed on inner circumferential sides of distal end portions of wall surfaces that face in a tool rotation direction of helically twisted chip discharge flutes, which is formed on an outer circumference of a distal end portion of a tool body that is rotated around the axis. End cutting edges are formed on a distal end of the main gash faces. Sub gash faces has an angle of inclination with respect to the axis that is greater than that of the main gash faces. The sub gash faces are formed on an outer circumferential side of the main gash faces such that they extend away via step portions from the main gash faces. In addition, corner cutting edges that have a protruding arc-shaped contour are formed to be continuous with an outer circumferential side of the end cutting edges extending from a distal end as far as an outer circumference of the sub gash faces.

TECHNICAL FIELD

This is a U.S. National Phase application under 35 U.S.C. §371 of International Patent Application No. PCT/JP2003/016477, filed Dec. 22, 2003, and claims the benefit of Japanese Patent Application No. 2002-375687, filed Dec. 26, 2002 and 2002-375688, filed Dec. 26, 2002, all of which are incorporated by reference herein. The International Application was published in Japanese on Jul. 15, 2004 as WO 2004/058438 A1 under PCT Article 21(2).

BACKGROUND OF THE INVENTION

An example of a radius end mill that is used in the machining of a work piece in which a corner cutting edge, in which an end cutting edge and a peripheral cutting edge intersect, is formed in a convex arc shape is disclosed in Japanese Unexamined Patent Application, First Publication No. S59-175915.

As is shown in FIG. 31, in this radius end mill there is provided an end mill in which end cutting edges 2 are positioned at a distal end of a tool body 1 and peripheral cutting edges 3 are positioned at a predetermined twist angle θ₁ on an outer circumference of the tool body 1. In this end mill, a twist angle θ₂ of corner cutting edges 4 in the vicinity of a corner of the edge tip is smaller than the twist angle θ₁ of the peripheral cutting edges 3 that are connected to the corner cutting edges 4. In addition, a corner R is provided on the corner cutting edges 4. In this type of radius end mill, because the small twist angle θ₂ is provided in the vicinity of a distal end of the corner cutting edges 4, the edge tip corner does not form an extremely acute angle, and working of the corner R is simplified while accuracy may be maintained. In addition, there are no defects in the edge due to the thinness of the edge tip corner portion. Moreover, because the portions of the peripheral cutting edges 3, which are the centers of the machining, are provided with a large twist angle θ₁, which has excellent machining properties, materials that are difficult to machine such as titanium alloys and stainless steel may be machined easily and with a high degree of accuracy. Furthermore, it is possible to achieve a marked improvement in reducing tool costs and in the processing efficiency of the milling tasks.

However, in this radius end mill, because the twist angle θ₂ of the corner cutting edges 4, which are provided with a corner R, on the distal end side of the peripheral cutting edges 3 is made weak, namely, because the rake angle in the axial direction of the corner cutting edges 4 and the end cutting edges 2 that are connected to the corner cutting edges 4 and extend to the inner circumferential side is small, although the included angle of the end cutting edges 2 and corner cutting edges 4 may be enlarged and it is possible to prevent defects, as is described above, it is not possible to prevent the blunt. Whereas, if, for example, the depth of a cut is shallow, and the center of the cut is not on the peripheral cutting edge 3 side but is on the end cutting edge 2 side, then because the distance from the center axis O of the tool body 1 is short on the inner peripheral side of the end cutting edges 2, the cutting speed is slow. Accordingly, the load during the cutting is increased and greater edge tip strength is required. In contrast, because the cutting speed is fast at the corner cutting edges 4 on the outer peripheral side of the end cutting edges 2, the load during the cutting is light, and, instead of greater edge tip strength, what is required is a sharp cutting edge. However, in a radius end mill in which the axial direction rake angle is small extending from the end cutting edges 2 to the corner cutting edges 4, in the manner described above, on the contrary, there is a possibility that there will be an increase in the cutting resistance.

Moreover, in particular, if a slanted metal surface or curved metal surface is cut using this type of radius end mill, because a number of the corner cutting edges 4 that are provided with the corners R in the vicinity of the edge tip corners thereof are used, if the sharpness of the edges in portion such as this is poor and there is considerable cutting resistance, then there is no possibility of achieving an improvement in the processing efficiency. Furthermore, in the above described conventional radius end mill, because the peripheral cutting edges 3 that are connected to the corner cutting edges 4 are provided with twist angle gradual increase portions 5 that extend from the twist angle θ₂ to the large fixed twist angle θ₁ so that the twist angle is made to change gradually, and because, in conjunction with this, the rake faces that are continuous with the cutting edges 4 are also formed as smoothly continuous faces whose incline gradually changes, shavings that are produced by the corner cutting edges 4 are discharged in an elongated form along these rake faces, and the problem also arises that there is a deterioration in the ability to process these chips.

Furthermore, FIG. 32 is an enlarged view showing principal portions of this conventional radius end mill. Corner portions 6, which are convex on the corner cutting edge 4 side, are formed on rake faces 2A and 4A as a result of an inner edge 2B (i.e., a boundary line between the rake face 2A and a wall face that protrudes outwards on the front side in the rotation direction T of the tool from the rake face 2A) of the rake face 2A of the end cutting edge 2 and an inner edge 4B (i.e., a boundary line between the rake face 4A and a wall face that protrudes outwards on the front side in the rotation direction T of the tool from the rake face 4A) of the rake face 4A of the corner cutting edge 4 intersecting at an obtuse angle.

However, in this type of radius end mill, a shortening of the interval from the end cutting edges 2 and corner cutting edges 4 to the inner edges 2B and 4B that corresponds to the size of the corner portions 6, which are intersecting portions between the inner edges 2B of the rake faces 2A of the end cutting edges 2 and the inner edges 4B of the rake faces 4A of the corner cutting edges 4, may not be avoided. In conjunction with this, because it also becomes impossible to ensure a sufficiently large space for the discharging chips, the problem arises that there is deterioration in the ability to discharge the chips.

In particular, in a radius end mill in which a ratio r/D between a radius of curvature “r” of substantially arc-shaped portions formed by the corner cutting edges 4, which constitute the intersection portions (i.e., corner portions) between the peripheral cutting edges 3 and the end cutting edges 2, and a diameter D of the tool body 1 is set to 0.2 or more, or in a radius end mill in which the radius of curvature “r” of the substantially arc-shaped portions formed by the corner cutting edges 4 is set to (D−d)/2 or more with respect to the diameter D and the web thickness “d” of the tool body 1, because the corner cutting edges 4 are enlarged and there is a tendency for the interval from the end cutting edges 2 and corner cutting edges 4 to the inner edges 2B and 4B to be reduced, the above described problem of there being a deterioration in the ability to discharge the chips is conspicuous.

Moreover, in the corner portions 6 in which the inner edges 2B and 4B intersect with each other, the chips easily become caught up and the presence of the corner portions 6 causes a further deterioration in the ability to discharge the chips.

DISCLOSURE OF INVENTION

The present invention was conceived from this background and it is an object thereof to provide a radius end mill that enables a high degree of sharpness to be imparted to a protruding arc-shaped corner cutting edge that has a corner R provided on an outer circumferential side thereof, while enabling sufficient edge tip strength to be secured on the inner circumferential side of an end cutting edge, and that also achieves an improvement in the ability to dispose of chips produced by this corner cutting edge.

In order to achieve these objects, in the present invention, chip discharge flutes that are helically twisted are formed on an outer circumference of a distal end portion of a tool body that is rotated around an axis, main gash faces whose angle of inclination with respect to the axis is a smaller angle than a twist angle of the chip discharge flutes are formed on inner circumferential sides of distal end portions of wall surfaces of the chip discharge flutes that face in the direction of rotation of the tool; and the end cutting edges are formed on a distal end of the main gash faces, and sub gash faces whose angle of inclination with respect to the axis has been made greater than that of the main gash faces are formed on an outer circumferential side of the main gash faces such that they extend away via step portions from the main gash faces. In addition, the corner cutting edges that have a protruding arc-shaped contour are formed so as to be continuous with an outer circumferential side of the end cutting edges from a distal end as far as an outer circumference of the sub gash faces.

Accordingly, in a radius end mill that is structured in this manner, because main gash faces that are inclined with respect to the axis at a smaller angle than the twist angle of the chip discharge flutes are formed on inner circumferential sides of distal end portions of the chip discharge flutes, and because end cutting edges are formed on the distal ends thereof, the included angle of the end cutting edges may be increased, and it is possible to secure a cutting edge strength that is sufficient to withstand a large cutting load such as that described above. In addition to this, because sub gash faces whose angle of inclination with respect to the axis has been made greater than that of the main gash faces are formed on an outer circumferential side of the main gash faces and protruding arc-shaped corner cutting edges are formed on outer circumferential portions of the distal end of the sub gash faces, the rake angle in the axial direction of these corner cutting edges may be made larger than that of the end cutting edges, so that they are provided with excellent sharpness. Moreover, because the sub gash faces that are continuous with the corner cutting edges and form the rake faces thereof are made to extend away via step portions from the main gash faces that form the rake faces of the end cutting edges, and because, as a result of this, the chips that are produced by the corner cutting edges may be made to collide against these step portions, resistance may be imparted to the chips before they are discharged in an elongated shape, so as to curl or break them, thereby improving the ability to dispose of the chips.

However, if the step portions between the main gash faces and the sub gash faces are formed, for example, so as to be perpendicular to the sub gash faces, then the chips that are produced by the corner cutting edges as is described above create blockages when they collide against these step portions, so that the chip discharge performance is deteriorated and, conversely, there is a possibility that the smooth disposal of the chips will be obstructed. Therefore, it is desirable that the step portions be formed as inclined surfaces that move gradually away as they move from the main gash face side towards the sub gash face side.

Moreover, it is desirable that an angle of inclination of the inclined surfaces formed by the step portions in this case be within a range of 30° to 60° with respect to a direction that is perpendicular to the sub gash faces. If this angle of inclination is less than 30° and the rise in the step portions is a steep gradient, then there is a possibility that it will not be possible to sufficiently prevent the aforementioned blockages of chips from occurring. If, on the other hand, the inclination is a gentle slope that exceeds 60°, then the possibility arises that it will not be possible to impart sufficient resistance to collided chips and achieve reliable disposal.

Furthermore, when the step portions are formed as inclined surfaces in this manner, these inclined surfaces may be planar surfaces that have a constant angle of inclination, however, if the inclined surfaces are formed as concave curved surfaces, it becomes easier to curl the collided chips and more reliable chip disposal may be achieved.

A further object of the present invention is to provide a radius end mill that enables chips to be disposed of in an excellent manner.

In order to achieve this object, in the present invention, in a radius end mill in which end cutting edges and substantially arc-shaped corner cutting edges are formed on a tool body that is rotated around an axis, inner edges of rake faces of the end cutting edges and inner edges of rake faces of the corner cutting edges are formed as a single, smoothly continuous convex curve.

In the present invention that is constructed in this manner, because inner edges of rake faces of the end cutting edges and inner edges of rake faces of the corner cutting edges are formed as a single, smoothly continuous convex curve, and because, unlike the conventional structure, there are no corner portions produced by the inner edges intersecting each other formed on these rake faces, it is possible to increase the spacings between the end cutting edges and the corner cutting edges and the inner edges of the rake faces thereof by the amount obtained by obviating these corner portions. Namely, by securing a large enough space for discharging chips, it is possible to maintain an excellent chip disposal performance.

Furthermore, in the same manner, because the inner edges of the rake faces of the end cutting edges and corner cutting edges together form a single continuous convex curve, when produced chips are discharged, it is difficult for these chips to become caught, and the chips may be discharged smoothly. Because of this as well, it is possible to maintain an excellent chip discharge performance.

It is also preferable that a rake face of an end cutting edge and a rake face of a corner cutting edge are formed as a single, smoothly continuous curved surface. By forming a rake face of an end cutting edge and a rake face of a corner cutting edge as a single, smoothly continuous curved surface, produced chips are able to pass smoothly over these rakes faces, resulting in a further improvement in the chip discharge performance being achieved.

The present invention enables a considerable effect to be expected in cases such as when a ratio r/D between a radius of curvature “r” of the substantially arc shapes formed by the corner cutting edges and the diameter D of the tool body is set to 0.2 or more, or when the radius of curvature “r” of the substantially arc-shaped portions formed by the corner cutting edges is set to (D−d)/2 for the diameter D and the core thickness “d” of the tool body, namely, in cases when the corner cutting edges are large and it is necessary to have a small spacing between the corner cutting edges and end cutting edges and the inner edges of the rake faces of these edges.

BRIEF DESCRIPTION DRAWINGS

FIG. 1 is a plan view of a distal end portion of a tool body 11 showing a first embodiment of the present invention,

FIG. 2 is a side view of the embodiment shown in FIG. 1,

FIG. 3 is a front view as seen from the distal end in a direction of an axis O of the embodiment shown in FIG. 1, and

FIG. 4 is a cross-sectional view taken along the line Z-Z in FIG. 1.

FIG. 5 is a plan view of a distal end portion of a tool body 11 showing a second embodiment of the present invention,

FIG. 6 is a side view of the embodiment shown in FIG. 5,

FIG. 7 is a front view as seen from the distal end in a direction of an axis O of the embodiment shown in FIG. 5, and

FIG. 8 is a cross-sectional view taken along the line Z-Z in FIG. 5.

FIG. 9 shows a third embodiment of the present invention, and corresponds to the cross-sectional view taken along the line Z-Z in FIG. 5.

FIG. 10 is a plan view showing a fourth embodiment of the present invention,

FIG. 11 is a cross-sectional view of a distal end portion (i.e., a cross-sectional view taken along the line Y-Y in FIG. 12) of a tool body 11 of the embodiment shown in FIG. 10, and

FIG. 12 is a front view as seen from the distal end in a direction of an axis O of the embodiment shown in FIG. 10.

FIG. 13 to FIG. 15 show an indexable insert 33 that is mounted on the embodiment shown in FIG. 10, and FIG. 13 is a plan view, FIG. 14 is a side view, and FIG. 15 is a front view.

FIG. 16 and FIG. 17 show a clamp mechanism 34 of the embodiments shown in FIGS. 10 and 25, and FIG. 16 is a cross-sectional view taken along the line Z-Z in FIGS. 10, 12, 25, and 27, and FIG. 17 is a cross-sectional view taken along the line Z-Z in FIG. 16 (the indexable insert 33 and clamp screw 42 are omitted from the drawings).

FIG. 18 is a plan view of a radius end mill according to a fifth embodiment of the present invention,

FIG. 19 is a side view of a radius end mill according to the fifth embodiment of the present invention,

FIG. 20 is a view of a distal end surface of a radius end mill according to the fifth embodiment of the present invention, and

FIG. 21 is a cross-sectional view of a tool body 50 of a radius end mill according to the fifth embodiment of the present invention.

FIG. 22 is a plan view of a radius end mill according to a sixth embodiment of the present invention,

FIG. 23 is a side view of a radius end mill according to the sixth embodiment of the present invention, and

FIG. 24 is a view of a distal end surface of a radius end mill according to the sixth embodiment of the present invention.

FIG. 25 is a plan view showing a seventh embodiment of the present invention,

FIG. 26 is a cross-sectional view of a distal end portion (i.e., a cross-sectional view taken along the line Y-Y in FIG. 27) of the tool body 11 of the embodiment shown in FIG. 25,

FIG. 27 is a front view as seen from the distal end in the direction of the axis O of the embodiment shown in FIG. 25.

FIG. 28 to FIG. 30 show an indexable insert 60 that is mounted on the embodiment shown in FIG. 25, FIG. 28 is a plan view, FIG. 29 is a side view, and FIG. 30 is a front view.

FIG. 31 is a plan view of a conventional radius end mill,

FIG. 32 is an enlarged view of principal portions of the conventional radius end mill shown in FIG. 31.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described with reference made to the drawings. It should be understood, however, that the present invention is not limited to these embodiments and, for example, various combinations of component elements of the embodiments may be made as is appropriate.

Firstly, FIGS. 1 through 17 show first through fourth embodiments of the present invention that relate to a radius end mill in which a main gash face having an end cutting edge is formed on an inner peripheral side of a distal end portion of a wall surface of a chip discharge flute of a tool body, and in which sub gash faces are formed via a step portion on an outer peripheral surface of the main gash face, and corner cutting edges are formed extending from the distal end of the sub gash faces to an outer circumference.

Of these, in the first embodiment of the present invention which is shown in FIGS. 1 through 4, a tool body 11 is formed from a hard material such as cemented carbide having a circular column-shaped external configuration that is centered on an axis O. Note that the tool body 11 is formed so as to have a rotationally symmetric configuration around the axis O.

A pair of chip discharge flutes 12 are formed on an outer circumference of a distal end portion (i.e., the end portion of the left side in FIGS. 1 and 2) of the tool body 11 such that, as they move from the distal end towards the rear end side, they are helically twisted at a constant twist angle α around the axis O towards the rear in the rotation direction T of the tool during a cutting operation.

Wall faces 13 of the chip discharge flutes 12 that face in the tool rotation direction T are formed at a cross-section that is orthogonal to the axis O as concave curved surfaces that are depressed towards the rear side of the tool rotation direction T. Peripheral cutting edges 14 are formed on side ridge portions on the outer circumferential side of the wall faces 13, while end cutting edges 15 are formed on the distal end side of the wall faces 13. Furthermore, corner cutting edges 16 having an arc-shaped external configuration that protrude towards the outer circumferential side at the distal end are formed so as to be connected to the peripheral cutting edges 14 and the end cutting edges 15 on corner portions on the outer circumferential side of the distal end of the wall faces 13 where the peripheral cutting edges 14 and end cutting edges 15 intersect.

Here, in the present embodiment, gashes are formed in two stages on inner and outer circumferences of the distal end portion of the wall faces 13 that face towards the tool rotation direction T of the chip discharge flutes 12. Of these, a main gash face 17 is formed by the first stage gash on an inner circumferential side of the wall face 13, and the end cutting edge 15 is formed on a distal end edge of the main gash face 17.

The main gash faces 17 are formed in a planar shape by cutting out the inner circumferential side of the distal end portion of the wall face 13 in a direction that is substantially parallel to the axis O. Accordingly, the angle of inclination of the main gash faces 17 with respect to the axis O is set to 0°, and is set as smaller than the twist angle α of the chip discharge groves 12. As is shown in FIG. 3, the end cutting edges 15 are formed so as to extend rectilinearly towards the outer circumferential side from the inner circumference of the tool body 11 as seen from the distal end in the axial direction O, and are provided with a rake angle of 0° in the axial direction that is the same as the aforementioned angle of inclination.

However, in the present embodiment, as seen in plan view facing the main gash faces 17, the end cutting edges 15 are slightly inclined so as to approach the distal end side as they move towards the outer circumferential side, as shown in FIG. 1, thereby resulting in the end cutting edges 15 being provided with a concave angle.

On the outer circumferential side of the distal end portion of the wall face 13, sub gash faces 18 are formed on an inner side of the aforementioned corner portion by the second stage gash so as to be adjacent to the outer circumferential side of the main gash face 17. The corner cutting edges 16 are formed on side ridge portions on the outer circumferential side of the distal ends of the sub gash faces 18.

The sub gash faces 18 are formed in the same manner as the main gash faces 17 by cutting the outer circumferential side of distal end portions of the wall faces 13 in a planar shape. However, while the main gash faces 17 extend substantially in parallel to the axis O, as is described above, at points of intersection P between the end cutting edges 15 and the corner cutting edges 16, the sub gash faces 18 intersect with the main gash faces 17 and are slanted so as to gradually extend away towards the rear side of the tool rotation direction T with respect to the main gash faces 17 as they approach the rear end side in the direction of the axis O. Accordingly, an angle of inclination β of each sub gash face 18 with respect to the axis O is made larger on the positive angle side than the angle of inclination with respect to the axis O of the main gash faces 17 which is 0°.

Moreover, by forming the sub gash faces 18 such that they extend away from the main gash faces 17, the sub gash faces 18 are made adjacent to the main gash faces 17 via a step portion 19. In the present embodiment, at a cross-section that is orthogonal to the axis O, as shown in FIG. 4, these step portions 19 are formed as planar wall surfaces that are perpendicular to the main gash faces 17. In addition, they are also perpendicular to the sub gash faces 18. Furthermore, as shown in FIG. 1, at the aforementioned point of intersection P, the step portions 19 are made to intersect with the end cutting edges 15 and corner cutting edges 16, so that they extend substantially perpendicularly with respect to the end cutting edges 15 that have been provided with the aforementioned concave angle.

Moreover, the angle of inclination β of the sub gash faces 18 with respect to the axis O is made smaller than the twist angle α of the chip discharge flutes 12 with respect to the axis O. Accordingly, as shown in FIG. 1, at rear ends of these sub gash faces 18, outer circumferential ends of an intersection edge line L where the main gash faces 17 intersect with the wall faces 13 are made to intersect with the wall faces 13 at the point where they pass the rear end side, and an outer circumferential end of an intersection edge line M thereof is taken as an intersection point Q between the peripheral cutting edges 14 and the corner cutting edges 16. However, if the sub gash face 18 is small, this type of structure does not need to be employed.

Note that because the wall faces 13 are formed as the above described concave curved surfaces, in the above described plan view, the intersection edge lines L and M are formed as convex curved lines that protrude towards the distal end side, as shown in FIG. 1.

Moreover, while the corner cutting edges 16 make smooth contact at the intersection points P with the end cutting edges 15 that are formed as straight lines, as they approach the outer circumferential side at the rear end along the protruding arcs formed by the corner cutting edges 16 from the intersection points P, they are inclined so as to approach the rear end side of the rotation direction T to match the angle of inclination β of the sub gash faces 18, and intersect with the peripheral cutting edges 14 at the intersection point Q.

Accordingly, in a radius end mill that is constructed in this manner, firstly, the main gash faces 17, which form an angle of inclination that is smaller (i.e., 0°) with respect to the axis O than the twist angle α of the chip discharge flutes 12, are formed on an inner circumferential side of the distal end portion of the wall faces 13 that face in the tool rotation direction T of the chip discharge flutes 12, and the end cutting edges 15 are subsequently formed on the distal ends of these main gash faces 17. Accordingly, compared with when the wall faces 13 are simply extended as they are towards the distal end side so as to form end cutting edges, the included angle of the end cutting edges 15 may be increased. As a result, in the end cutting edges 15 in which, on the inner circumferential side of the tool body 11, the cutting speed is slow and a considerable cutting load is applied, a sufficient edge tip strength may be secured, and it is possible to lengthen the lifespan of the tool by preventing chipping or defects from occurring in the cutting edge.

On the other hand, because the sub gash faces 18, which are inclined towards the rear in the tool rotation direction T as they approach the rear end side at the angle of inclination β with respect to the axis O that is larger than that of the main gash faces 17, are formed in a distal end portion of the wall faces 13 on the outer circumferential side of the main gash faces 17, and because the substantially protruding arc-shaped corner cutting edges 16 that are continuous with the outer circumferential sides of the end cutting edges 15 are formed on side ridge portions of the outer circumferential sides of the distal ends of the sub gash faces 18, the corner cutting edges 16 may be provided with excellent sharpness, and a decrease in cutting resistance may be achieved. Accordingly, in particular, in a cutting operation to cut a slanted surface or curved surface of a mold in which the corner cutting edges 16 are frequently used, an improvement in the cutting efficiency may be achieved.

Moreover, in the present embodiment, although the angle of inclination β of the sub gash faces 18 is greater than that of the main gash faces 17, it is smaller than the twist angle α of the chip discharge flutes 12. Accordingly, compared with when the corner cutting edges are formed by simply extending the wall faces 13 as they are as far as the distal end of the tool body 11, a larger included angle may be secured in the corner cutting edges 16, and it is possible to prevent chipping or defects occurring in the corner cutting edges 16.

Moreover, as a result of the sub gash faces 18, whose angle of inclination β with respect to the axis O is different from that of the main gash faces 17, being formed at distal end portions of the wall faces 13 by making the end cutting edges 15 and corner cutting edges 16, which are formed at the distal end sides of the gash faces, smoothly continuous at the intersection points P, the sub gash faces 18 are made to extend away from the main gash faces 17, and the above described step portions 19, which are shaped as vertical wall surfaces standing upright from the sub gash faces 18, are formed between the sub gash faces 18 and the main gash faces 17. In addition, because the step portions 19 are formed so as to extend substantially perpendicularly from the intersection points P to the end cutting edges 15, namely, so as face the outer circumferential side of the tool body 11, chips that are produced in portions extending, in particular, from corner portion protruding ends to the outer circumferential sides of the corner cutting edges 16 during a cutting operation to cut an inclined surface or curved surface of a die or the like, may be made to slide along the top of the sub gash faces 18 and collide with the step portions 19.

As a result, even if the chips are discharged in elongated form, because they are subjected to resistance by when they collide against the step portions 19 and undergo processing such as being curled or broken, according to a radius end mill having the above described structure, an improvement in the processing ability of these chips may also be achieved, and together with a reduction in the cutting resistance of the corner cutting edges 16, it becomes possible to achieve a smoother die cutting operation and the like.

Note that, in the above described first embodiment, in a cross-section where the step portions 19 intersect the axis O, they are perpendicular to the main gash faces 17 and are also perpendicular to the sub gash faces 18. Accordingly, it is possible to provide greater resistance to the chips that have collided with the step portions 19 and a reliable processing thereof may be achieved. However, on the other hand, if the angle of the step portions 19, which form upright wall shapes in the manner described above, with respect to the sub gash faces 18 is a steep gradient, then, depending on the cutting conditions and the like, the chips that have been discharged onto the sub gash faces 18 in the manner described above may not only be subjected to resistance when they collide against the step portions 19, but the discharge itself may be obstructed and blockages produced. This may cause an interruption of a smooth chip discharge and, conversely, there is a possibility that the chip processing capability will be deteriorated.

Therefore, in cases such as this, as in the radius end mill of a second embodiment of the present invention shown in FIGS. 5 through 8, it is desirable that step portions 20 be formed as inclined surfaces that gradually extend away as they approach the sub gash face 18 side from the main gash face 17 side. Note that, in the second embodiment shown in FIGS. 5 through 8, portions that are the same as in the first embodiment shown in FIGS. 1 through 4 are given the same reference symbols and a description thereof is omitted.

Here, in the same manner as the step portions 19 of the first embodiment, as shown in FIG. 5, the step portions 20 of the second embodiment are formed so as to extend from the intersection point P between the end cutting edges 15 and the corner cutting edges 16 in a substantially perpendicular direction with respect to the end cutting edges 15. However, unlike in the first embodiment in which the step portions 19 are also perpendicular to the main gash faces 17 and sub gash faces 18, as shown in FIG. 8, at a cross section where they intersect with the axis O, the step portions 20 are formed as planar inclined faces that extend away from the main gash faces 17 at a constant angle of inclination as they move from the main gash faces 17 towards the sub gash faces 18. Moreover, in the present embodiment, as shown in FIG. 8, the angle of inclination of the inclined surface produced by the step portion 20 having the constant angle is set within a range of 30 to 60° as an angle of inclination γ with respect to a direction that is perpendicular to the sub gash face 18 at a cross section that intersects the axis O.

Accordingly, in the radius end mill of the second embodiment that is formed in this manner, because the step portions 20 are formed as inclined faces that gradually extend away as they move from the main gash faces 17 side towards the sub gash face 18 side in the manner described above, the gradient of the step portions 20 as seen from the sub gash face 18 side is more gentle than that of the step portions 19 of the first embodiment. Accordingly, even if chips produced at the corner cutting edges 16 are discharged along the sub gash faces 18 and collide with the step portions 20, they are subjected to resistance by the step portions 20 and while being either curled or broken, are guided along the slope of the inclined surface formed by the step portion 20, and may be reliably discharged without causing any blockages.

Moreover, in the present embodiment, the angle of inclination γ of the inclined surfaces formed by the step portions 20 are set within a range of 30 to 60° with respect to a direction that is perpendicular to the sub gash face 18. As a result, as is described above, chip blockages may be reliably prevented and a smooth discharge achieved, while at the same time sufficient resistance is imparted to the chips and smooth processing of the chips, such as the curling or breaking thereof, may be achieved. Here, if the rise of the step portions 20 is a steep gradient so as to approach the vertical resulting in the angle of inclination γ being reduced so as to be less than 30°, then there is a possibility of it not being possible to sufficiently prevent chip blockages. If, however, the inclination is flattened so that the angle of inclination γ is more than 60°, then the resistance that is imparted to collided chips is too small, and there is a possibility that reliable processing will not be obtainable.

In this second embodiment, the step portions 20 are formed as planar inclined surfaces having a constant angle of inclination γ, however, as in a third embodiment which is shown in FIG. 9, it is also possible to form step portions 21 as concave curved surfaces, and to make the angle of inclination of the step portions 21 with respect to a direction that is perpendicular to the sub gash face 18 gradually smaller as it moves from the sub gash face 18 side to the main gash face 17 side. Note that FIG. 9 is a view corresponding to the cross section taken along the line Z-Z in FIG. 5 of the second embodiment, and portions that are the same as those in the second embodiment are given the same reference symbols.

Accordingly, in this third embodiment as well, because the step portions 21 are formed as inclined surfaces that are gradually extend away as they move from the main gash face 17 side to the sub gash face 18 side, the same effects as those of the second embodiment may be obtained. In addition, because the inclination as seen from the sub gash face 18 side becomes a gradually steeper gradient as it moves towards the main gash face 17 side, while chips that are discharged over the sub gash face 18 collide at first against the gentle gradient portion of the step portion 21 so that blockages may be reliably prevented, they are then pushed as they are so as to be guided to the steep gradient portion of the main gash face 17 side and gradually become subject to resistance. As a result, they are more efficiently curled or broken, and disposed of. Namely, according to the radius end mill of the third embodiment, this radius end mill is more effective in that it achieves both the excellent chip disposal performance of the first embodiment and the smooth chip discharge performance of the second embodiment.

Next, FIGS. 10 through 17 show a fourth embodiment when the present invention, in which the sub gash faces 18 are formed via the step portions 19, 20, and 21 on the outer circumferential side of the main gash faces 17 in the manner described above, is applied to a throw away type of radius end mill. Note that, in this fourth embodiment as well, component elements that are the same as in the above first through third embodiments are given the same reference symbols and the description thereof is abbreviated.

Namely, in the first through third embodiments, the chip discharge flutes 12, main and sub gash faces 17 and 18, step portions 19, 20, and 21, peripheral cutting edges 14, end cutting edges 15, and corner cutting edges 16 are formed directly on the circular cylinder-shaped tool body 11 that is formed from a hard material such as a cemented carbide. However, in the fourth embodiment, the tool body 11 is constructed by forming an insert mounting seat 32 at a distal end portion of a circular cylinder-shaped holder 31, and removably mounting an indexable insert 33 on this insert mounting seat 32 using an insert clamp mechanism 34. The above described chip discharge flutes 12, main and sub gash faces 17 and 18, step portions 19, 20, and 21, peripheral cutting edges 14, end cutting edges 15, and corner cutting edges 16 are formed on the indexable insert 33. Note that the holder 31 is formed from a steel material or the like, and the indexable insert 33 is formed from a hard material such as cemented carbide.

Here, a distal end portion of the holder 31 is formed in a hemispherical shape. The insert mounting seat 32 is formed as a concave groove that extends in one direction that is orthogonal to the axis O by cutting the distal end portion of the holder 31 along a plane that includes the axis O of the tool body 11 such that it is open on the distal end side. The insert mounting seat 32 is formed by a pair of wall surfaces 35 and 36 that are parallel with the axis O and are also parallel with each other such that they face each other, and an end surface 37 that is perpendicular to the wall surfaces 35 and 36 and is also perpendicular to the axis O while facing the distal end side of the holder 31.

The indexable insert 33 is formed in a substantially quadrangular planar shape that is able to be fitted into the concave groove-shaped insert mounting seat 32. The indexable insert 33 is provided with a pair of side surfaces 38 and 39 that are parallel to each other and are in tight contact with the wall surfaces 35 and 36 when the indexable insert 33 has been fitted, and with a rear end surface 40 that is perpendicular to the side surfaces 38 and 39 and is in tight contact with the end surface 37. Furthermore, a mounting hole 41 having a circular cross section that penetrates the indexable insert 33 substantially in the center thereof perpendicularly to the side surfaces 38 and 39 is formed between the side surfaces 38 and 39.

When the tool body 11 has been formed by fitting the indexable insert 33 into the insert mounting seat 32 and fixing it in position using the clamp mechanism 34, chip discharge flutes 12 are formed respectively in a spiral configuration on a pair of circumferential surfaces of the indexable insert 33 that are positioned on an outer periphery of the distal end portion of the tool body 11. In addition, peripheral cutting edges 14 are formed at side ridge portions on the outer circumferential side of the wall surfaces 13 that face the tool rotation direction T side, the main gash faces 17 are formed on an inner circumferential side at the distal end, and the end cutting edges 15 are formed at side ridge portions on the distal end side thereof. The sub gash faces 18 are formed via the step portions 19, 20, or 21 on the outer circumferential side of the main gash faces 17. Convex arc-shaped corner cutting edges 16 are formed on the side ridge portions extending from the distal end of the sub gash faces 18 to the outer periphery thereof.

When an indexable insert 33 that has been fitted into the insert mounting seat 32 is positioned such that a center line X of the mounting hole 41 is orthogonal to the axis O of the tool body 11, and is fixed in place by the clamp mechanism 34, and when the tool body 11 has been constructed in this manner, a symmetrical configuration is formed around the axis O. Moreover, out of the hemispherical distal end portion of the holder 31, that portion that is adjacent to the tool rotation direction T side of the pair of chip discharge flutes 12 of the indexable insert 33 is formed as a notched portion 31A by a cylindrical surface whose radius is greater than the radius of this hemisphere.

Accordingly, in the indexable insert type of radius end mill of the fourth embodiment as well in which the peripheral cutting edges 14, the end cutting edges 15, the corner cutting edges 16, the main gash face 17, the sub gash face 18, and the step portions 19, 20, and 21 are formed on the indexable insert 33, it is possible to obtain the same effects as in the first through third embodiments in accordance with the form of the step portions 19, 20, and 21.

In the clamp mechanism 34 of the present embodiment, by screwing a clamp screw 42 that is inserted from one side (i.e., the wall surface 36 side) of the distal end portion of the holder 31 that is separated into the wall surface 35 side and the wall surface 36 side with the insert mounting seat 32 in-between and penetrates the indexable insert 33 to reach the other side (i.e., the wall surface 35 side) in order to clamp the indexable insert 33 that has been fitted into the insert mounting seat 32, not only is the distal end portion of the holder 31 elastically deformed so as to sandwich the indexable insert 33, but the clamp screw 42 itself is also elastically deformed and is bent in a direction that intersects the screwing-in direction. As a result, the indexable insert 33 is pushed in the bending direction and is clamped.

Here, the clamp screw 42 has a male thread portion 42A at one end thereof and has a flat countersunk head portion 42B whose underside is in the form of a cone at the other end thereof. Between the male threaded portion 42A and the head portion 42B is formed a columnar shaft portion 42C that has an external diameter that enables it to be press-fitted inside the mounting hole 41, and has an axial length that is slightly longer than the gap between the wall surfaces 35 and 36 of the insert mounting seat 32.

Moreover, in one of the portions of the distal end portion of the holder 31, which is separated by the concave groove-shaped insert mounting seat 32, that is on the wall surface 35 side (i.e., the aforementioned portion on the other side) of the insert mounting seat 32 is formed a screw hole 43 that penetrates this portion so as to be perpendicular to the wall surface 35. The screw hole 43 is formed so as to be coaxial with the center line X of the indexable insert 33 that has been positioned in the manner described above. The portion of this screw hole 42 that opens onto the wall surface 35 is formed as a cross-sectionally circular hole 43A that has the same internal diameter as the mounting hole 41 of the indexable insert 33, and is formed such that the end portion on the male threaded portion 42A side of the shaft portion 42C of the clamp screw 42 is able to be press-inserted therein. A female threaded portion 43B into which the male threaded portion 42A of the clamp screw 42 is threaded is formed in the portion on the opposite side from the wall portion 35 that is beyond the circular hole 43A.

In that portion of the distal end portion of the holder 31 that is on the wall surface 36 side (i.e., the aforementioned portion on the one side) of the insert mounting seat 32 as well is formed a through hole 44, into which the clamp screw 42 is inserted, perpendicularly to the wall surface 36 so as to penetrate that portion. This through hole 44 is an elongated hole that is formed such that, at any position in the center line X direction of the indexable insert 33 that has been positioned in the manner described above, a cross-section thereof that is parallel to the wall surface 36 is in the shape of an elongated hole having a major axis that extends in a direction that is parallel to the axis O, as shown in FIG. 17, namely, in a direction that intersects the center line X direction in which the clamp screw 42 is threaded. Moreover, the center of that half arc portion of the circumference of the ellipse that is on the distal end side (i.e., the left side in FIG. 17) of the tool body 11 is positioned on the center line X, and this distal end side half arc portion and the rear end side half arc portion are connected together by a pair of tangent lines at both ends of these half arcs that are in parallel with the major axis and also in parallel with each other.

Furthermore, the portion of the through hole 44 that opens onto the wall surface 36 is set to the same size as the inner diameter (i.e., the diameter) of the half arc of the ellipse formed by the aforementioned cross section, and the gap between the pair of tangent lines, namely, the width W of the ellipse is set to the same size as the inner diameter (i.e., the diameter) E of the circular hole 43A of the screw hole 43 of the wall surface 35 on the opposite side and as the inner diameter (i.e., the diameter) of the mounting hole 41 in the indexable insert 33, and the shaft portion 42C of the clamp screw 42 is formed as an engaging portion 44A that has a width that enables it to be 

1. A radius end mill in which end cutting edges and substantially arc-shaped corner cutting edges are formed on a tool body that is rotated around an axis, comprising: chip discharge flutes, which are helically twisted, formed on an outer circumference of a distal end portion of the tool body; main gash faces whose angle of inclination with respect to the axis is a smaller angle than a twist angle of the chip discharge flutes, said main gash faces formed on inner circumferential sides of distal end portions of wall surfaces of the chip discharge flutes that face in a direction of rotation of the tool, the end cutting edges formed on a distal end of the main gash faces; and sub gash faces whose angle of inclination with respect to the axis has been made greater than that of the main gash faces, said sub gash faces formed on an outer circumferential side of the main gash faces such that they extend away via step portions from the main gash faces, wherein the corner cutting edges that have a protruding arc-shaped contour are formed so as to be continuous with an outer circumferential side of the end cutting edges from a distal end as far as an outer circumference of the sub gash faces.
 2. A radius end mill according to claim 1, wherein step portions between the main gash faces and the sub gash faces are formed as inclined surfaces that move gradually away as they move from the main gash face side towards the sub gash face side.
 3. A radius end mill according to claim 2, wherein an angle of inclination of the inclined surfaces formed by the step portions is within a range of 30° to 60° with respect to a direction that is perpendicular to the sub gash faces.
 4. A radius end mill according to claim 2, wherein the inclined surfaces are formed as concave curved surfaces.
 5. A radius end mill in which end cutting edges and substantially arc-shaped corner cutting edges are formed on a tool body that is rotated around an axis, wherein: inner edges of rake faces of the end cutting edges and inner edges of rake faces of the corner cutting edges are formed as a single, smoothly continuous convex curve.
 6. A radius end mill according to claim 5, wherein the rake face of the end cutting edge and the rake face of the corner cutting edge are formed as a single, smoothly continuous curved surface.
 7. A radius end mill according to claim 5, wherein a ratio r/D between a radius of curvature “r” of the substantially arc-shaped portions formed by the corner cutting edges and the diameter D of the tool body is set to 0.2 or more.
 8. A radius end mill according to claim 5, wherein the radius of curvature “r” of the substantially arc-shaped portions formed by the corner cutting edges is set to (D−d)/2 or more for the diameter D and the web thickness “d” of the tool body.
 9. A tool body having a radius end mill in which end cutting edges and substantially arc-shaped corner cutting edges are formed on the tool body that is rotated around an axis, comprising: chip discharge flutes, which are helically twisted, formed on an outer circumference of a distal end portion of the tool body; main gash faces whose angle of inclination with respect to the axis is a smaller angle than a twist angle of the chip discharge flutes, said main gash faces formed on inner circumferential sides of distal end portions of wall surfaces of the chip discharge flutes that face in a direction of rotation of the tool, and the end cutting edges formed on a distal end of the main gash faces; and sub gash faces whose angle of inclination with respect to the axis has been made greater than that of the main gash faces, said sub gash faces formed on an outer circumferential side of the main gash faces such that they extend away via step portions from the main gash faces, and wherein the corner cutting edges that have a protruding arc-shaped contour are formed to be continuous with an outer circumferential side of the end cutting edges from a distal end as far as an outer circumference of the sub gash faces.
 10. A radius end mill according to claim 9, wherein step portions between the main gash faces and the sub gash faces are formed as inclined surfaces that move gradually away as they move from the main gash face side towards the sub gash face side.
 11. A radius end mill according to claim 10, wherein an angle of inclination of the inclined surfaces formed by the step portions is within a range of 30° to 60° with respect to a direction that is perpendicular to the sub gash faces.
 12. A radius end mill according to claim 10, wherein the inclined surfaces are formed as concave curved surfaces. 